532 CIRCULATION OF BLOOD AND LYMPH. 



before entering the capillary regions, but as a result of dilatation in 

 the arteries of an organ the pulse may carry through and appear in 

 the veins, in which it may be shown, for instance, by the rhythmical 

 flow of .blood from an opened vein. The term venous pulse, how- 

 ever, as generally used applies to an entirely different phenomenon, 

 namely, to a pulse observed especially in the large veins (jugular) 

 near the heart. The pulse in this case is not due to a pressure wave 

 transmitted through the capillaries, but to pressure changes t of 

 both a positive and negative character occurring in the heart or 

 the neighboring arteries and transmitted to the veins. The venous 

 pulse that has this origin may usually be seen and recorded in the 

 external (or internal) jugular. Under pathological conditions, espe- 

 cially when the flow through the right heart is more or less impeded, 

 it may be plainly apparent at a further distance from the heart and 

 may cause a noticeable pulsation of the liver, which is designated as 

 a liver pulse. The venous pulse curve has been much studied in 

 recent years.* It is somewhat complicated and an explanation 

 of some of its details has not been agreed upon, but there can be no 

 doubt that when properly interpreted it will throw much light upon 

 the pressure changes in the heart, and will afford a valuable means 

 of diagnosis in cases of valvular lesions and other pathological 

 conditions of the heart. It is evident also that the venous pulse 

 gives a ready means of determining the rate of beat of the auricles, 

 just as the arterial pulse enables us to count the beats of the ven- 

 tricles, and in this way records of the venous pulse are important 

 in the interpretation of irregularities in the beat of the heart 

 (arrhythmia). 



As usually recorded the venous pulse shows three positive 

 waves, designated commonly as the a, c, and v waves, and three 

 negative waves. Of the three positive waves, the a wave marks, 

 undoubtedly, the contraction of the auricle, but in order to 

 locate this wave or, indeed, to interpret at all the complicated 

 venous pulse, it is necessary to have a simultaneous tracing of 

 the arterial pulse, preferably the carotid, or of the apex beat of 

 the heart. Either of these latter tracings enables one to mark 

 upon the venous pulse the point at which the ventricular systole 

 begins, and the wave immediately preceding this point must 

 be due to the auricular contraction, the a wave (Figs. 217 and 

 218). Following the rise of the a wave there is a fall, the first 

 negative wave, which is due to the auricular relaxation. The 

 interpretation of the other two positive and negative waves 

 has been the subject of much discussion. Mackenzie, one of 

 whose tracings is reproduced in Fig. 217), believed that the 



*See Mackenzie, " The Study of the Pulse," 1902; also Lewis, in Hill's 

 " Further Advances in Physiology," New York, 1909. 



